An improved method and apparatus for retreading or recapping worn tire carcasses is shown in the assignee's U.S. Pat. No. 4,274,897. This patent discusses many of the difficulties attendant with prior retreading systems, and the disclosed method and apparatus for retreading tires overcomes many of the past problems. In the aforementioned patent an envelope is used to encompass the tread and tire carcass sides, and the envelope is sealed to the tire sides by grills wherein the envelope is sealed to the tire during vulcanization.
While the use of the envelope locates the envelope adjacent the tread marginal edges wherein the uncured bonding material between the tread and carcass is exposed such that the envelope aids in shaping the transition zone between the tread and tire side, the flexibility of the envelope, and the lack of firm substantial shaping surfaces at the transition zone, often results in bubbles, smears, and other nonuniform deviations which detract from the appearance of the finished product.
Further, use of the envelope during pressurization and heating within the vulcanization chamber does not permit the pressures imposed upon the tread to be uniform, especially within the grooves of the tread configuration, and a uniform bonding and vulcanization pressure is difficult to achieve. Further, the need to assemble the envelope to the tread and tire carcass prior to vulcanizing complicates the vulcanizing process adding costs, and considerable skill is required by the operator to correctly correlate the envelope with the grills which seal the envelope to the tire carcass sides.
It is an object of the invention to provide a method and apparatus for retreading tires with a molded tread where a layer of bonding material is interposed between the tread and prepared tire carcass wherein the transition zone between the tread and tire side uniformly blends into the tire side for improved bonding and aesthetic purposes.
Another object of the invention is to provide a method for retreading tires utilizing a bonding material between a tread and the tire carcass wherein the marginal edges of the tread and the bonding material, are, alone, confined during vulcanization of the tread to the tire.
A further object of the invention is to provide apparatus for use during the retreading of tires engaging the marginal edge of the tread and the tire side during vulcanization to iron and shape the transition region to improve the appearance and mechanical properties thereof.
An additional object of the invention is to provide tire retreading apparatus adapted to engage the transition region between a tire carcass side and the tread marginal edge during vulcanization for shaping the marginal region, and wherein the iron used for such shaping is adjustably mounted upon a substantially rigid support permitting self-alignment of the iron to the tire side.
A further object of the invention is to provide a method and apparatus for vulcanizing a tread upon a tire carass by means of a bonding material which does not require inflation or internal support of the tire carcass, nor requires an envelope surrounding the tread and engaging the tire sides.
Yet another object of the invention is to provide apparatus for retreading tires which does not require encasement of the tread within an envelope nor inflation or support of the tire carcass, and wherein equal external pressures are applied to the tread during pressurization within the vulcanizing chamber.
In the practice of the invention a precured profiled tread of annular configuration is placed upon a prepared tire carcass with uncured bonding material interposed therebetween. The marginal edges of the tread and bonding material lie upon the tire side and are externally accessible and visible.
A pair of grills are each associated with an annular iron and are mounted upon opposite sides of the tire assembly and pulled toward each other by bridging springs.
The iron is preferably formed of an elastomeric material and is associated with circular wire rings concentric to the tire carcass axis. The iron includes an ironing surface of a concave configuration substantially corresponding to the tire side configuration and the iron is preferably associated with the wire rings in a loose manner wherein the iron and iron surface may slightly move relative to the ring and closely align itself with the tire side contour.
The iron and ironing surface are of sufficient mass, and radial dimension, as to overlie the transition region between the tire tread and the tire carcasses, including the bonding material therebetween, and as the grill ring supports the elastomer iron throughout its form, the ironing surface will be uniformly and closely held against the tire side and tread marginal edge.
Upon placing the assembled tire carcass, tread and grills within a vulcanization chamber such as an autoclave, the soft bonding material, due to the heat, will be shaped by the ironing surface, as is the tread marginal edge, and a smooth blending of the tread edge, bonding material and tire carcass side occurs "under" the ironing surface whereupon, upon removal of the grill and iron from the tire side, an attractive retreading appearance is achieved, and the ironing surface improves the mechanical features of the transition region by minimizing bubbles, loose or unvulcanized edges, and the like.
The configuration of the grills is such that a plurality of tire and grill assemblies may be stacked within a conventional autoclave to permit a plurality of tires to be simulaneously vulcanized reducing the time and expense of retreading.